This is a proposal for continued support to study the development of pathways, connections, and neuronal morphology in the visual system using triploid animals, i.e. animals each of whose cells contains three sets of chromosomes instead of two. In work done under an initial grant, the retina and tectum of triploid frogs were shown to contain larger but fewer cells than diploids, so that the overall size of these structures is similar in the two types of animals. Therefore, eye transplants between diploids and triploids will result in a disparity between retinal and tectal tissue that, in contrast to previous attempts to induce disparities, should not be complicated by an inherent tendency for compensatory "regulation" of the affected tissue. I propose now to make such eye exchanges and to study the resulting hybrid visual systems, with emphasis on two question: (1) How is the retinotectal projection affected by the altered number of optic nerve fibers from the transplanted eye? and (2) How do the structure and function of individual nerve cells in the visual system depend on their own ploidy and on interaction with tissue of a different ploidy? Triploids are produced by subjecting fertilized eggs to a hydrostatic pressure shock. Eye rudiments from each embryo will be exchanged with a rudiment from an individual of different ploidy. After metamorphosis, the retinotectal projection from both the normal and transplanted eyes will be mapped electrophysiologically. To measure the effect of optic nerve input on tectal locus specificity, the nerves will be deflected surgically to the ipsilateral tectum, and the projection will be mapped again. Extrinsic effects on neuronal morphology will be measured by receptive field analysis of single neurons and Golgi staining of cells in the tectum. A parallel set of transplants will be carried out using eyes from haploid frogs. The results of these experiments will provide tests of several theories about the growth of nerve fiber pathways and the development of neuron morphology.